Diastereoselectivity in the addition of allylzinc reagents to delta-alkoxy-gamma,delta-disubstituted alkenyllithium compounds.

The carbometalation reaction of allyl- and crotylzinc bromide with metalated disubstituted homoallylic ethers gives tri- or tetrasubstituted 5-hexenyl ethers with excellent control of the diastereoselectivity. The stereochemistry of this reaction is discussed and has been attributed to an early transition state with chelation to the oxygen atom in the energetically favored conformer as the stereodetermining step.

Diastereoselective and Enantioselective Intramolecular Amino-Zinc-Enolate Carbometalation Reactions. A New Polysubstituted Pyrrolidines Synthesis.

The amino-zinc-enolate cyclization allowed a new and straightforward route to polysubstituted pyrrolidines from simple starting materials. From this study, we have been able to determine, for the first time, the stereochemical influence of the substituents on the ring in the carbocyclization reaction. The diastereoselectivity thus obtained was explained by a chairlike amino-zinc-enolate transition state.

Amino Zinc Enolate Carbocyclization Reactions. New Access to Polysubstituted Piperidine Derivatives.

Various N-pent-4-enylglycine methyl esters have been submitted to carbocyclization of their zinc enolates onto the unactivated double bond. The cyclization to substituted pipecolic esters is highly stereoselective. In most cases, substitution of the pent-4-enyl moiety on various sites leads to a single isomer, hence a way to di-, tri-, tetra-, or pentasubstituted piperidines.